90 



CKEMICAL TRANSFORMATIONS. 



in a certain order, otherwise both friction i 

 and motion would be without the smallest 

 influence. 



The simple permanence in position of the 

 atoms of a body, is the reason that so many 

 compounds appear to present themselves, in 

 conditions, and with properties, different 

 from those which they possess, when they 

 obey the natural attractions of their atoms. 

 Thus sugar and glass, when melted and 

 cooled rapidly, are transparent, of a con- 

 choidal fracture, and elastic and flexible to a 

 certain degree. But the former becomes 

 dull and opaque on keeping, and exhibits 

 crystalline faces by cleavage, which belong 

 to crystallized sugar. Glass assumes also 

 the same condition, when kept soft by heat 

 for a long period ; it becomes white, opaque, 

 and so hard as to strike fire with steel. 

 Now, in both these bodies, the compound 

 molecules evidently have different positions 

 in the two forms. In the first form their at- 

 traction did not act in the direction in which 

 their power of cohesion was strongest. It 

 is known also, that when sulphur is melted 

 and cooled rapidly by throwing it into cold 

 water, it remains transparent, elastic, and 

 so soft that it may be drawn out into long 

 threads ; but that after a few hours or days, 

 it becomes again hard and crystalline. 



The remarkable fact here is, that the 

 amorphous sugar or sulphur returns again 

 into the crystalline condition, without any 

 assistance from an exterior cause ; a fact 

 which shows that their molecules have as- 

 sumed another position, and that they pos- 

 sess, therefore, a certain degree of mobility, 

 even in the condition of a solid. A very 

 rapid transposition or transformation of this 

 kind is seen in arragonite, a mineral which 

 possesses exactly the same composition as 

 calcareous spar, but of which the hardness 

 and crystalline form prove that its molecules 

 are arranged in a different manner. When 

 a crystal of arragonite is heated, an interior 

 motion of its molecules is caused by the ex- 

 pansion ; the permanence of their arrange- 

 ment is destroyed ; and the crystal splinters 

 with much violence, and falls into a heap 

 of small crystals of calcareous spar. 



It is impossible for us to be deceived re- 

 garding the causes of these changes. They 

 are owing to a disturbance of the state of 

 the equilibrium, in consequence of which 

 the particles of the body put in motion obey 

 other affinities or their own natural attrac- 

 tions. 



But if it is true, as we have just showii 

 it to be, that mechanical motion is sufficient 

 to cause a change of condition in many 

 bodies, it cannot be doubted that a body in 

 the act of combination or decomposition is 

 capable of imparting the same condition of 

 motion or activity in which its atoms are to 

 certain other bodies : or in other words, to 

 enable other bodies with which it is in con- 

 tact to enter into combinations, or suffer de- 

 compositions. 



The reality of this influence has been al- 



ready sufficiently proved by the facts de- 

 rived from inorganic chemistry, but it is of 

 much more frequent occurrence in the re- 

 lations of organic matter, and causes very 

 striking and wonderful phenomena. 



By the terms fermentation, putref action f 

 and eremacausis, are meant tnose changes ia 

 form and properties which compound or- 

 ganic substances undergo when separated 

 from the organism, and exposed to the in- 

 fluence of water and a certain temperature. 

 Fermentation and putrefaction are examples 

 of that kind of decomposition, which we 

 have named transformations : the elements 

 of the bodies capable of undergoing these 

 changes arrange themselves into new com- 

 binations, in which the constituents of water 

 generally take a part. 



Eremacausis (or decay) differs from fer- 

 mentation and putrefaction, inasmuch as it 

 cannot take place without the access of air, 

 the oxygen of which is absorbed by the de- 

 caying bodies. Hence it is a process of 

 slow combustion, in which heat is uni- 

 formly evolved, and occasionally even light. 

 In the processes of decomposition termed 

 fermentation and putrefaction, gaseous pro- 

 ducts are very frequently formed, which are 

 either inodorous, or possess a very offensive 

 smell. 



The transformations of those matters 

 which evolve gaseous products without 

 odour are now, by pretty general consent, 

 designated by the term fermentation ; whilst 

 to the spontaneous decomposition of bodies 

 which emit gases of a disagreeable smell, 

 the term putrefaction is applied. But the 

 smell is of course no distinctive character 

 of the nature of the decomposition, for both 

 fermentation and putrefaction are processes 

 of decomposition of a similar kind, the one 

 of substances destitute of nitrogen, the other 

 of substances which contain it. 



It has also been customary to distinguish 

 from fermentation and putrefaction a par- 

 ticular class of transformations, viz., those 

 in which conversions and transpositions are 

 effected without the evolution of gaseous 

 products. But the conditions under which 

 the products of the decomposition present 

 themselves are purely accidental ; there is 

 therefore no reason for the distinction just 

 mentioned. 



CHAPTER III. 



FERMENTATION AND PUTREFACTION. 



SEVERAL bodies appear to enter sponta 

 neously into the states of fermentation and 

 putrefaction, particularly such as contain 

 nitrogen or azotised substances. Now, it is 

 very remarkable, that very small quantities 

 of these substances, in a state of fermenta- 

 tion or putrefaction, possess the power of 

 causing unlimited quantities of similar mat- 

 ters to pass into the same state. Thus, a 



